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#21
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The "List Number" in this case 8055 and the revision number -1 for your carb. The Carb # is for a 1971-1972 Chevy engine. There is also a carb with the number 8051-1 that is also for a Chevy. Look at your numbers again. You have one too many numbers. 8051 or 8055? Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#22
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Vacuum secondary spread-bores used a 6.5 Power Valve so yours has the 6.5 and does not need changing unless leaking due to backfire damage. Again, it would run so poorly it would be obvious. The double pumper used an 8.5 Primary power valve and 6.5 secondary which is where I got that 8.5 number from.
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Triple Black 1971 GTO |
#23
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Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#24
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My Holley Book for list numbers is obviously out of date for a carb with that high of number.
So the carb, even though it is a spread bore, was built MUCH later than I assumed. Sorry for the confusion. The web posts say that some are not happy with that carb. 2 stars out of 5 should tell you something. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. Last edited by Tom Vaught; 10-20-2021 at 03:39 PM. |
#25
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I was able to increase the vacuum from 14 to 16 inches by adjusting the idle mixture screws. Still getting a heavy gasoline smell out of the exhaust.
I have not been able to figure out what the heck is going on with engine timing, however. I have the vacuum advance disconnected and have capped the port on the carb that it connects to. Measuring manifold vacuum from the intake manifold fitting. I have turned the distributor as much as I dare (at this point) to advance the timing, but the timing is still way beyond TDC. The idle speed did not change much as I advanced the timing, and that has me curious. I have never seen timing so far out of adjustment and am afraid I'm missing something critical here. Yes I verified I'm on plug #1. There is only one scribe mark on the harmonic balancer. Any ideas?
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Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#26
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Is the mechcanical advance in the distributor brining in more timing with the rev’s above 1500?
If you look down into each primary throttle bore with the motor at idle do you see fuel dribbling out of the booster?
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#27
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I can't explain the timing but it shouldn't even be able to run at 25 ATDC.
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Triple Black 1971 GTO |
#28
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exactly my thinking... something's off
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Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#29
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I note that since I've advanced the timing from where it was, it runs rougher but has more overall power. No sign of pinging. Thinking maybe my timing light is acting up?
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Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#30
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Check your harmonic balancer, too. The ring could have moved.
It was mentioned once, but you need to confirm that the timing mark is indeed at TDC for cylinder #1. If the mark is off, everything else is moot.
Have you tried to just turn the distributor until the timing is actually at 8* BTDC with the vacuum advance disconnected and plugged? You will probably need to turn your idle speed down if you do this, and then readjust the idle mixtures, too. Just curious..... |
#31
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I did turn the distributor more and got the timing close to TDC, but the idle actually decreased rather than increased as I would have expected. Idle is noticeably rougher and car just runs like crap. Will readjust idle mixture and see what I get.
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Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#32
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Verifying the mark on the balancer is correct is a little more complicated.
You will need a helper to do this.
Remove the spark plug from cylinder #1. Put a big socket and breaker bar (or a really long ratchet) on the crankshaft/balancer retaining bolt. Turn the crankshaft clockwise (when viewed from the front) until the timing mark on the balancer starts coming up from below the timing marks/numbers on the timing cover. Try to stop at about 5 or 6 o'clock. Have your helper hold his/her finger pretty firmly over the spark plug hole for #1. They will feel either suction or pressure at different points as you rotate the crankshaft. That's normal. Keep rotating the crankshaft clockwise. As the timing mark on the balancer rotates up, your helper should feel pressure pushing his/her finger off the spark plug hole if the cylinder is on the compression stroke. There is a 50/50 chance this will happen the first time you come up on the marks. If there is no pressure, cylinder #1 is on the exhaust stroke. Rotate the crankshaft one complete rotation and do it again. If you visualize the harmonic balancer as a clock, with the timing marks at about 10 o'clock, the pressure should start at around 5 o'clock as you rotate the crankshaft. You may have to repeat this a couple times to make sure you're on the compression stroke. When you are on the compression stroke for #1, the pressure should build up just until you get to the 0* timing mark on the timing cover. As you pass 0*, the pressure should change to suction and pull your helper's finger against the hole. This does not mean that the pressure instantly changes to suction. Work the crankshaft up to the 0* mark and pause until the pressure bleeds off. Then keep turning the crankshaft clockwise and see if any more pressure builds up. If the pressure continues to build after you pass the 0* mark and then starts sucking in approximately the area where you are now seeing the timing mark when the engine is running, the harmonic balancer is bad and the outer ring has slipped. Hopefully my explanation is not too confusing...... If you're not sure your timing light is functioning right, you may want to borrow a known good light and verify. Or put your light on a known, correctly timed engine and see what is indicated. Good luck! |
#33
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Having the Rotor point at TDC when on the timing mark many times means you are probably one tooth off on the distributor installation. It has to be pointed before the
the #1 terminal and you need to know that a Pontiac distributor rotor moves counter clockwise. But you probably already know all that. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#34
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Question for the OP here.
Your rotating the distributor and having it run ruff and have the rpm drop is a sure fire sign that your turning the thing the wrong way! The rotor in these motors spin counter clockwise, so to advance the timing you need to spin the distributor towards the driver side of the car. If your going things right you should be able to rotate it far enough that the starter will not be able to crank the motor over.
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#35
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__________________
Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#36
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__________________
Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#37
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__________________
Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#38
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Well No Wonder.....
So I guess I should trust my instincts more. Turns out the PO had intentionally retarded the timing in order to get it to run halfway decent with a bad carburetor.
Took the car in to a local mechanic and he discovered that the idle mixture screw for the left bank is broken / has no effect. He also verified the crazy timing setting and set it back to 8 BTDC as it should be. Car now really runs like crap. Off to buy a replacement carburetor. Many thanks to all who have helped me work through this.
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Mark Las Cruces NM ___________________________ Current Project: '67 Catalina Convertible 400 4-spd |
#39
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Did the mechanic say anything about the metal covering the EGR ports? The way the mixture screws work on that carb, a bad vacuum leak would make a screw non-functional. Did the mechanic verify TDC on the balancer. Did the mechanic blow out or clean air bleed holes to try and get that mixture screw to work? Slowing initial timming for a bad carb makes no sense at all. That would just make things worse. Need to verify the TDC mark and then, if needed, pull a valve cover and check "cam timing". It can be looked at on cylinder 1 or 6 during overlap. We can get you plenty of directions on here for that. Clay |
#40
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I missed this......
Posted by QUICK SILVER
Did the mechanic say anything about the metal covering the EGR ports? The way the mixture screws work on that carb, a bad vacuum leak would make a screw non-functional. I never paid that close of attention to the pic and didn't notice that piece of metal..........it looks pretty primitive and I don't know how it would ever seal the passages correctly. Here's a suggestion that won't cost too much: Pull off the carb. Tape off the intake openings with blue tape. Remove that piece of metal covering the EGR ports. I can't even guess at how it is secured..... Either get a REAL EGR block-off plate and gasket from Edelbrock (or someone like that). Even better, put expansion plugs into the two holes under the metal piece. You should be able to measure them approximately and then go buy $20 worth of plugs at NAPA or somewhere similar. Use the two that fit and take the others back. Remove the blue tape, reinstall the carb and see how it runs. I wish you were closer to Vega$ - we've got a half-dozen known good carbs (Holleys, AFBs and quadrajets) just for situations like this. We'd swap one on and see how it runs. Usually take about forty-five minutes to diagnose and pinpoint the problem. Good luck! |
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